White House Chief of Staff Reince Priebus says that Trump's immigration ban will not affect anyone with a green card. However, border agents will have "discretionary authority" to hold or question anyone they deem suspicious.

The announcement came less than 48 hours after Trump barred all refugees from entering the United States for four months to keep out "radical Islamic terrorists."

The order Friday immediately suspended a program that last year resettled in the U.S. roughly 85,000 people displaced by war, political oppression, hunger and religious prejudice. Trump indefinitely blocked those fleeing Syria, where a civil war has raged, and imposed a 90-day ban on all immigration to the U.S. from seven Muslim majority nations, citing terrorism concerns.

"We want to ensure that we are not admitting into our country the very threats our soldiers are fighting overseas," Trump said as he signed the order at the Pentagon. "We only want to admit those into our country who will support our country and love deeply our people."

Trump said the halt in the refugee program was necessary to give agencies time to develop a stricter screening system. While the order did not spell out what additional steps he wants the departments of Homeland Security and State to take, the president directed officials to review the refugee application and approval process and find any more measures that could prevent those who pose a threat from using the refugee program.

The U.S. may admit refugees on a case-by-case basis during the freeze, and the government will continue to process requests from people claiming religious persecution, "provided that the religion of the individual is a minority religion in the individual's country."